Simultaneous synthesis of a biogas process and heat exchanger network

This paper presents an energy efficient synthesis of the biogas process, performed simultaneously with the synthesis of its heat exchanger network (HEN). Its overall superstructure is composed of i) the process and ii) the HEN superstructure, and linked with iii) a proposed process stream superstructure where streams could be mixed into a smaller number of hot and cold streams, in order to obtain simpler and, yet, energy efficient solutions. The combined synthesis problem is formulated as a mixed-integer nonlinear programming (MINLP) problem. The model consists of an MINLP model for the biogas process and a modified MINLP model for the simultaneous synthesis of heat-integrated HEN . It enables the selection of an optimal biogas process scheme with an optimal arrangement of its HEN. The synthesis, as applied to an existing large-scale meat company, yielded a complete energy self-sufficient solution for thermophilic biogas production, closed-loop water configuration, and simple HEN arrangement.